This invention relates to magnetic recording media such as magnetic recording tapes, floppy disks, magnetic recording disks, etc., a process for producing the same, and magnetic memory apparatuses using the magnetic recording media, and more particularly to magnetic recording media for longitudinal recording suitable for high density magnetic recording, a process for producing the same and magnetic memory apparatuses.
Heretofore, magnetic recording media using a metallic magnetic film have been proposed as magnetic recording media for longitudinal recording for high density magnetic recording, as disclosed in Japanese Patent Publication No. 54-33523. Processes for forming magnetic recording media for longitudinal recording include an evaporation process, a sputtering process, a plating process, an ion beam sputtering process, etc.
Recently, needs for higher density recording and higher reliability have been increased. For example, magnetic recording media for longitudinal recording with a thin metallic magnetic film having an inplane coercivity as high as about 700 Oe and a high corrosion resistance at a high temperature and a high humidity, such as thin metallic magnetic film of magnetic alloy, e.g. Co--Pt, Co--Cr--Pt, Co--Ta--Pt, Co--Si--Pt, Co--Zr--Pt, Co--Hf--Pt, etc. have been proposed as in Japanese Patent Applications Kokai (Laid-open) Nos. 60-111323, 59-177725, 59-8806, etc.
Furthermore, it has been proposed to improve static magnetic properties such as an inplane coercivity Hc, a squareness S. a coercive squareness S*, etc. For example, it has been proposed to form a pure metal layer of Cr, Mo, W, Nh, W, etc. or an alloy layer of Cr--V, Cr--Fe, etc. as an underlayer on a substrate and form a magnetic recording layer of Co--Pt alloy or Co--Cr--Pt alloy thereon, an disclosed in Japanese Patent Application Kokai (Laid-open) No. 62-257617 (=U.S. Pat. No. 4,654,276), or to form a magnetic recording layer of Co--Cr--Pt alloy on a Ni--P underlayer, as disclosed in Japanese Patent Application Kokai (Laid-open) No. 59-88806, or to form an alumite underlayer on a substrate of aluminum alloy and form a magnetic recording layer of cobalt (Co)-based alloy comprising 3 to 15 at. % of at least Mo, V and W, 3 to 20 at. % of Cr and 3 to 15 at. % of a noble metal element such as Pt, Rh, Ru, Re, Pd, Ir, etc., the balance being at least 75 at. % of Co, thereon, as disclosed in Japanese Patent Applications Kokai (Laid-open) Nos. 61-246917 and 61-253622.
Furthermore, Japanese Patent Application Kokai (Laid-open) No. 62-257617 (=U.S. Pat. No. 4,654,276) and Japanese Patent Application Kokai (Laid-open) No. 62-257618 (=U.S. Pat. No. 4,652,499) disclose that when a magnetic recording layer of Co--Pt or Co--Cr--Pt is produced on a nonmagnetic underlayer having a thickness of about 50 nm, such as Cr--V underlayer or W underlayer, the inplane coercivity Hc can be made higher than 1,200 Oe and also the coercive squareness S* higher than 0.9.